Electrical protective device



1951 H. T. BUSSMANN Re. 23,315

ELECTRICAL PROTECTIVE DEVICE Original Filed April '25, 19-38 If A III! INVENTOR. HEMP) 2' BUJ'J'MANN ATTORNEY.

Reissued Jan. 2, 1951 ELECTRICAL PROTECTIVE. DEVICE '"Henry T. Bussmann, St'.-Louis','-Mo.

Original No. 2,275,403, dated'March 1011942; Se-

I rial No. 2'04;206',April 25,1938; Application for reissueMarch 23, IMZj-Serial- No; 435,910

"*Matterencloscd in.heavy brackets II appears inthe original patent bntforms nog'part ofthis reissuespecification; matter printed" in italics indicates the additions made by'reissue Claims.

1; 1 'My'invention' relates to protective devices for :electriccircuits designed to open-the circuit on excess currents 'which, it "continued; might -be "harmful.

Anmbject 'ofmy-invention isto provide a protector which will adequately protect against harr'nful overloads and" have such time-lag as to also protect against" interruption of service on T-harmful overloads.

- Another object -of"my-"invention is to-"provide expense-and annoyance of needless interruptions, 'should accordingly, carry small overloads for relativelylong times but blow quickly on heavy overloads "and almost instantly on short circuits.

-In-other' Words-the time lag of the protector should be comparable to, but somewhat'less than,

that ofthe circuit'to be protected.

" Protectors formotor'circuits require a greater -==time lag-than is-ordinarily' necessary 'for other circuits becauseof the" heavy starting currents of the motors. If a protector having'the time lag desirable for" motor'circuits ,be used on a --c-ircuit not requiringso much time lag no lessening' or protection will result. If; however, a de- -"to-be protectedcan be-obta-ined at less-cost than one-having an unnecessarily great time lag'there would -be advantage in using it.

Branch circuits such as are ordinarily protected by devices'of 151 or' amperel25 v'olt ratings.

.arefiexamples of circuits whichsdo notrequire the long time lags necessary in protectors for motor 1 circuits. 'I-'hereare very'few '125' volt-motors of :atingsxin this-range andJif any motors are used starting:"currents-bf' which could" be handled by :rprotective adevices having I less time"; lag than mnecessaryin protectors of these ratings for purely motor circuits.

' Bymy'invention I am able-to provide at low cost a protector suitable for use on such'circuits '-as-" described which hag a longtime-lag at low orovrloads; a quickeblowat higher overloads and a practic'allyfiinstantaneous blow r-on- -shortcira cuits.

' vice having an adequate time-lag'ior the circuit.

on circuits 'of this typeg they: are small ones the *i-ng, 'as m-ay be desired according to the condition -of overload in the circuit, protectors -have-been used' having 1 a therm'ally-controlled mechanieally-operable circuit interrupter and a fuselink -in the same device. The mechanical interrupter is designed to open with long time lags on overloads: up toa predetermined value and the fuse linlr'to open in shorttimes on overloads above this value and 1 virtually instantaneously: on short circuits.

In--my application, Serial No."6'76,500 now Patent No; 2,111,749, I have shown and described a a protective device of this type. My present in- I a view of a preferred form of protector embodywhich'provides adequate protection without the ing my=-invention, a part'of'the enclosure being cut away. -Fig; 2*sh-ows a cross-sectional view along the line' 2 -2 ofFigl 1.

" InFig 1 a hollow body member I ofinsulating +materia1 has a closure member 2 and contact terminals 3 and 4 thereon.

A fuse link, 5 and a --'thermally-controlled mechanically-operable circuit interrupter havingoperating means 1- are enclosed'w'ithinthe body member I and serve to electrically connectthecontact terminals 3 and 4.

The-interrupter also includes a movablecontact member 8 comprisingan' end portion of the fuse link 5; a heating element 9 and a mass of heat nect the link and the heating element.

inorder to make use of the excess mass of the softenable material I 0 normally holding the contact member 8 in electrical connection with the heating element 9.

- I use a muchlarger mass of the heat softenable material IEI'than-isrequired to electrically con- This is heat soitenable material as a means of increasing? the time lag. The greater the mass of'the heat 'softenable' material the more heatwill be required-to soften it and, consequently, the longer the blowing time at a given current. This increased' mass will slightly increase the minimum a material increasein timelag results.

In order to make use of a considerable quantity of-heat softenable material I prefer to interpose between the link and-the heating element a heat and electric conducting member H. This mem- '-beris iorm'edwith a passageway therethrough of size and shape to permit the end 8 of the fuse link and an end of the heating element to be inserted therein and there maintained in electrical connection by the heat softenable material. This member makes for ease in assembly and permits the use of a relatively large amount of the heat softenable material. It also absorbs heat and retards the rate of temperature rise of the heat softenable material to provide additional increase in time lag.

As the amount of heat lost from this heatabsorbing member to the walls of the body will vary with the areas of their respestive surfaces in contact, this member is so shaped that the area thereof which can contact the body wall is very small, for example it may have a thin flanged portion 12. The heat loss is thus kept small and greater uniformity of performance is obtained. This desirable characteristic more than compensates for any slight loss of time lag resulting from cutting down loss of heat to the body walls. I have found that the use of a relatively large quantity of heat softenable material without provision for restricting and rendering substantially uniform the conduction of heat therefrom to the walls of the body results in a lack of the uniformity of rating and blowing times essential in devices of the character of my invention.

The operating means 1, shown here as a helical spring, acts on the link at a point relatively near the heat softenable material which arrangement leaves the fusing portion of the link free from stress caused by the operating means. The other end of the operating means is so supported as to render the means substantially free from current flow therethrough.

The heating element 9 is a substantially fiat strip of metal usually having higher specific electrical resistance than that of the fuse link and of such dimensions relative to the fuse link that it will remain unfused at ordinary overloads though it may sometimes fuse on heavy short circuit. I prefer to stamp the element from sheet metal but may use a wire. It is of relatively large mass for the purpose, also, of retarding its rate of temperature rise on overload for a reason to be explained later. I may make it of such metals as brass, German silver, or others of lower or higher specific resistance, as I may prefer. I may, if desired, so form an end portion of the heating element as to constitute the equivalent of the solder cup II to facilitate connection thereto and permit the use of a sufficient quantity of heat softenable material to increase the time lag by absorbing a substantial amount of the heat, or make other minor changes in its shape Without departing from the simple form of the element as a Whole. I make the end which is soldered to the contact terminal wider than the main body of the element in order to minimize the effect on the rating which might be caused by a difference in height of the solder by means of which connection with the contact terminal 4 is maintained.

By making my heating element in this simple form I am enabled at low cost to provide for ease in connection to both the fuse link and the contact terminal. I make easy the use of a substantial amount of solder at the connection to the link in order to absorb a substantial quantity of heat and I can cheaply and efie'ctively counteract the effect of different solder heights at the connection to the terminal.

In order that the interrupter open as intended it is necessary that a certain amount Oi 1 .3%?

be generated in the heating element. If the heating element be formed of layers of wire wound close together the amount of metal therein to be heated will be relatively small, the one turn will tend to heat the adjacent turn and and radiation therefrom will be restricted. As a result the temperature rise will be relatively rapid. In a heating element such as used in my invention the mass of metal may be relatively great which makes for slower temperature rise. The cross-sectional area where connected to the contact terminal is relatively large which permits conduction of heat to the terminal. The element being substantially free from bends, radiation from one part of it can have substantially no effect on heating of a nearby part. The temperature of the heating element will accordingly rise slowly and a long time lag in the operation of the interrupter will result.

The fuse link 5 may be of any desirable material and may be of any desired. design. In a preferred form I use copper as that is a desirable material for use in fuse links, when as in this case, provision is made to prevent the attainment of too high a temperature on currents too low to blow the link.

It will be noted that when I use copper and brass or German silver for the link and heating element respectively, I use metals the specific resistances of which are relatively far apart while their melting points are relatively close together. I am enabled to use material of relatively similar melting points because by my construction the operation of the protector does not depend on the difference in melting points of these parts of the device. I may also, if I prefer, use materials of similar specific resistances by suitably proportioning dimensions.

The heat softenable material I8 may be a lowmelting point solder or alloy, in which case it can maintain the fuse link 5 and the heating element 5 in electrical connection with each other without the necessity of direct physical contact of link to element. On the other hand if the link and heating element are placed in direct physical contact with each other, or if both are in direct physical contact with the heat absorbing member II, the electrical connection thus established between them may be maintained by a heat softenable material which is not electrically conducting, as a wax for example.

0n the passage of a current through the device the heat softenable material I ll will be heated by the heating element and if the strength and duration of the current be sufficiently high this material will be softened to a degree where it will be unable to resist the force exerted by the operating means I. In this case the operating means I will withdraw the end of the link constituting the movable contact member 8 from its connection with the heating element 3 and interrupt the circuit.

In order that this operation take place with relatively long time lag the mass of the heating element is made relatively large. It is preferably connected directly to the contact terminal 3 for the same reason, as conduction of heat from the heating element to the terminal is a factor in retarding the rate of temperature rise of the heating element and hence, of the heat softenable material.

By thus retarding the temperature rise in the heating element by making its mass relatively large and by conducting heat away from it to the contact terminal, I provide a further method for i5 aicontrollingirtheaztime arofnoperationigbiizth wrotector. By proportioning the dimensions 'of these :members withwreference toatheir physic'aliachar- :1 acteristics Famf able to regulate the: 'amountxof -*-Istantial1ya:treesfromi tcurrenti: flowiztherethrough ,-:to:1break said seriesconnection by moving a portiomofth'e-tuse linkaway from the heating member when the-heat sot-tenable materiallhas been :heatzwhichrmust =be generated 'torisoftenithe heat -softenable material.

on higheri'overloads sthe "lime-will blovw-andsinte'rrupt"- the -circuit beforej" for the reasons- TjllSt Y given, the mechanical: interrupter can "operate.

delayed-i ope-ration" required at 1 low" overloads.

* While Izhaveshown and-described a preferred fir form- 0f, myinvention: and referred" to '-preferred materials which may be us'ed the'reim' it is ob- '=lvious*that modifications in form-and in- 'choice of r materials may be m'ade within the scopei oi my winvention.

'acwh'a't Ilcla'im' is:

,. 1; s In a: protector for electric circuits, a heating e1ement=having-formed ends and being substan- -tially- =prisrriatic in=shape l throughout the greater ---=-part= bf its lengthg said form'ed ends having a greater cross se'ctional area than has the 'pris- "tact with one of the foregoing elements near the endthereof to hold them inelectricalconnection with eachpther'and'adapted to "lose its holding r-cfuseilink-ihaving afusing" portion free'from-stress causedrby- :the circuitopening means.

2. A unitaryprotectorfor electric circuits comprising a casing, a fuse link, and a" thermallycontrolled mechanically operable circuit inter- -rupter irr the-casing; said' interrupter including a heat,absorbing-memberthaving a shape adapted to estrict to a negligible amount direct conduction f "heat-theretrom to the casing.

' 3. in a i protector for electric circuits comprising a casing, a iuselinkand av-mechanieally oper- 'ablethermal circuit interrupter in the casing, said, i' interrupter comprising a heating memberand a -heat-- absorbing member having a relatively thin =flangethereon extending outwardly beyond the heating me'mberand-adapted to'position the interrupter in thezcasing andrto -restrict conduction,

of heat to the casing.

A: A'protector for electric" circuits comprising acasing; a fuse 'link' and a mechanicallymp'erable thermal circuit interrupter in the casing, said interrupter including heat softenable material normally holding the interrupter in closed circuit position and adapted to lose its holding power when heated to a predetermined temperature, a heating element adapted to heat said heat softenable material, a member adapted to support a substantial quantity of said heat softenable material, to absorb heat and retard the rate of temperature rise of the heat softenable material, to position the interrupter in the casing, and to restrict and render substantially uniform the conduction of heat therefrom to the casing.

5. A plug type protector for electric circuits comprising a contact member in the bottom thereof, a contact member in the side wall thereof a heating member consisting of a metal stamping rigidlymounted on the bottom contact member, a fuse link in series connection with the heating member and the side contact member, heat softenable material normally maintaining said series connection, circuit-opening means sub- The prote'ctor. will: thusprovide the nuick 1 rfoper-l=.- :ationnecessary on high overloads asr well asthe heated to a predetermined temperature; "'a2nd isheat-absorbing' means arranged to conduct-heat t irom the heat softenable material to retard its "rate of temperaturerise, saidheating-member being 'free of bending? by if the circuit=opening 11053 means.

6;: A plug type protector for electric circuits 'compri'sing an enclosure of insulationmaterial, a

contact member in thebottom'of the enclosure, a

" con-tact member in a side wall thereof, a rigid me- :l5 -tallicheating member in' the enclosure relatively remote from the side walls thereof and fixedly mou'nted nn the bottom contact member', a 1 fuse link irrseries connection with the heating member-ahd theside contact member, heat softenable 220'" material normally maintaining said series connection; circuit-'opening' means "substantially free "from current flow th'erethrough arranged""--to break s'aid series-connection bymoving aporti'on --or the-fuse link awayfrom the h'eating member when the heat softenable material has been heat- --"ed 'toa; predetermined temperature, and heatabsorbing-"meansarranged to conduct heat from the-heat softenable material-to'retard its ratebf "--t'emperature' "rise.

'71 A plug protector forelectric circuits having a' cential opening; a-contact in the basethere'of, e a conta'ctin the side wall thereof; a metallic heating member, a heat-absorbing membery'and a -fuse ii nk "member in series connection with said" contacts; heat softenable material normally *co'nn'ectingtwo of-said members and a circuitopening member ='adapted to open" the circuit on softeningoi the heat softenable' material; the heatingmember and'the circuit-opening member being so arranged that the side-pull of' the "circuit snpe'ning member will be insubstantially the-same plane as the broader side ofthe heating member. I

8 In a-'protector for electric circuits; a casing,"

a fuse llink, heat 'sioftenable material normally ---ing-*means=out='of contact" with the wall of the" so casingwsaid member being so" arranged that *when inbontactwithsaid wall, it will 'afforda Y liinited heat-conducting path to said wall.

99 A protector for electric circuits foriningan enclosed structure and adapted to be inserted in P a fuse holder, said protector comprising a fuse link and a thermally-controlled mechanicallyoperable circuit interrupter, said interrupter including a heating element consisting of a metal stamping, and a heat-absorbing member intermediate the link and the heating element, said heating member having a cross-sectional area substantially less than that of the heat-absorbing member and being for the greater part of its length relatively remote from the walls of the enclosure.

10. A plug type protector for electric circuits that is an enclosed structure and is adapted to be inserted in a fuse holder, said protector comprising a casing having a thermally-controlled mechanically and thermally operable circuit interrupter therein, said casing having a recess therein and a terminal at its base, said interrupter comprising a fuse link member, a heating member having one of its ends fixedly secured to the said terminal and having its other end extending into the said recess, said heating member comprising a resistance element having a length of current path therethrough substantially equal to the over-all length thereof, a low melting point material on the end of the said heating member that extends into the casing formin a joint of said members, that normally umaintains an electrical connection between the fuse link member and the heating member, said heating member having a cross-sectional area that is quite small relative to the cross-sectional area of the said recess and a spring biasing the the fuse link to open circuit position.

11. In a plug type protector for electric circuits, a casing, a terminal in the base thereof, a

terminal in the sidewall thereof, a fuse link and a heating element in series relation between the terminals, said heating element being mounted on the base of the casing, a spring adapted to move the unsupported end of the heating element toward the side wall of the casing and a member mounted on the upper portion of the heating element toengage the wall of the easin and prevent movement of the heating element.

12. In a fusible protective device, a rigid metal heating conductor of relatively small mass an- I chored at one end, a relatively large heat absorbent mass electrically and mechanically connected to the otherend of said heating conductor and carried by said end, a flexible conductor,

a relatively small mass of readily fusible metal electrically connecting one end of said flexible conductor to said-heat absorbent mass, and means responsive to the fusing of said readily fusible metal to move said flexible conductor away from said heat absorbent mass, said heat absorbent mass being large as compared with the mass of said readily fusible metal to delay the fusing of the latter.

13. In a fusible protective device, a heatin conductor anchored at one end, a heat absorbent mass of relatively infusible metal electrically and mechanically connected to the other end of said heating conductor and supported thereby, a flea:-

ible conductor, a relatively readily fusible metal electrically connecting one end of said flexible conductor to said heat absorbent mass at a point remote from said heating conductor, and meansresponsive to the fusing of said readily fusible metal to move said flexible conductor away from said heat absorbent mass, said heat absorbent mass being large as compared with the mass of :said readily fusible metal to delay the 'fusing'of the latter.

14. In a fusible protective device, a rigid conductor comprising a heating element anchored at one end, a heat absorbent mass of electrical conducting material fixed to the other end of said conductor, a flexible conductor arranged to fuse when traversed by currents in excess of a predetermined value, a readily fusible mass electrically connecting one end of said flexible conductor to said heat absorbent mass at a point remote from said heating conductor, and means responsive to the fusing of said readily fusible mass to move said flexible conductor away from said heat absorbent mass.

15. in a fusible circuit interrupter, a rigid-supporting rod anchored at one end and having a hook at its other end, said supporting rod being formed of resistance material, a cylindrical plug formed of infusible electrical conducting material threaded on said hook, a-flexible conductona mass of readily fusible material for electrically connecting the heat absorbent mass to one end of said flexible conductor and arranged to release said flexible conductor from said mass of heat absorbent material upon the fusing thereof, and means responsive to the fusing of said readily fusible mass for separating said heat aborbing mass and said flexible conductor.

HENRY T. BUSSMANN.

REFERENCES CITED The following references are of record in the file of this patent or the original patent:

UNITED STATES PATENTS Number Name Date 953,393 Parkhurst Mar. 29, 1910 974,330 Aalborg Nov. 1, 1910 1,022,897 Stevens Apr. 9, 1912 1,276,567 Price Aug. 20, 1918 1,677,298 Sandin July 17, 1928 1,693,404 Sandin Nov. 27, 1928 2,111,749 Bussmann Mar. 22, 1938 2,113,155 Kiefer Apr. 5, 1938 2,168,815 Wood Aug. 8-, 1939 2,210,036 McEntee Aug. 6, 1940 2,218,274 Wood Oct. 15, 1940 FOREIGN PATENTS Number Country Date 587,795 Germany Nov. 8, 1933 

